Titanium is highly chemically durable in a living body and is highly biocompatible, and is therefore expected to be used as a bone substitute material. A bone substitute material to be implanted in a living body is desired to be porous because of the necessity to form bone or bond to surrounding bone in it. A titanium porous body is generally obtained by pressure-molding a titanium powder, which is mixed with a pore-forming material if necessary, to obtain a molded body and then sintering the molded body (see Patent Document 1). It is conventionally known that by bringing such a titanium porous body into contact with an aqueous alkali solution, it is possible to allow the surface of the titanium porous body to have the ability to form apatite (see Non-Patent Documents 1 and 2). Further, it is disclosed that artificial bone produced by forming a titanium porous body by plasma spraying, alkali-treating the titanium porous body in the same manner as described above, and immersing the alkali-treated titanium porous body in hot water has the ability to form bone in a living body even when it is implanted in an area where living bone does not exist (see Patent Document 2).
Patent Document 1: Japanese Patent Application Laid-open No. 2002-285203
Patent Document 2: WO 2004/062705A1
Non-Patent Document 1: J. Mater. Res., Vol. 17, No. 10, October 2002
Non-Patent Document 2: Biomaterials 25 (2004) 443-450